Zebrafish mbd5 Loss of Function Mutation Affect Embryonic Neuron Differentiation and Maturation

Background:  The prevalence of Autism spectrum disorders is growing rapidly within last decades with the etiology remains largely unknown. A newly identified member of methylated DNA binding domain protein family MBD5 has attracted substantial attentions recently, due to its causer role in 2q23.1 microdeletion syndrome. Patients with MBD5 haploid insufficiency display complex clinical symptoms including infantile ASD, EE, and craniofacial abnormalities. Mbd5 conditional knockout mouse die in preweaning stage, while heterozygous mutation mimicry features of 2q23.1 microdeletion syndrome, suggesting MBD5 might play critical role in nervous system during early embryonic developmental stage.

Objectives:  To further dissect the roles of MBD5 in nervous development and maturation, and the correlations between MBD5 mutations with neurological disorders like ASD.

Methods:  We choose Zebrafish as the animal model. Fish mbd5 expression was knocked down via injecting morpholino oligo affecting either ATG or RNA splicing. The development and morphology of fish embryo was closely monitored after injection. The expression of marker genes involved in neuron development and maturation was determined via whole amount in situ hybridization, qPCR and western blot. Fish behaviors were recorded and analyzed via Zebrafish Lab system.

Results:  

Knock down of fish mbd5 cause significant embryonic development delay, lethality, and morphological abnormalities in brain and cardiac vesicle that can be alleviated by co-injecting mbd5 cDNA constructs. Preliminary evidence indicated that mbd5 mutation disrupted the expression of critical genes regulating neuron maturation probably through affecting DNA methylation.

Conclusions: Disrupt mbd5 expression in Zebrafish cause embryonic development delay and lethality, which is consistent with the mouse model, suggesting the role of MBD5 in embryo development is conserved across species. The neuronal disorders caused by MBD5 insufficiency probably due to the misexpression of critical genes involved neuron differentiation and maturation, a mechanism depend on DNA methylation.